Wilson's warbler, Wilsonia pusilla, breeds in Alaska, Canada, the western United States, and parts of the extreme northeastern United States. It winters along parts of the Gulf Coast (Mississippi to Texas) and in Mexico and Central America south to Panama. In Utah, it is uncommon as a breeder in summer and common as a migrant. Its breeding habitat is riparian woodland and thickets near water (bogs, beaver ponds, etc.). On its wintering grounds, however, it utilizes a very wide range of habitats, including plains. Its foods are almost exclusively arthropods, but it occasionally consumes berries, and on its wintering grounds consumes honeydew produced by scale insects.
The nest is usually on the ground at the base of a tree or shrub, occasionally one or two feet above the ground in a shrub or small tree. The female parent incubates the two to seven (but most commonly four) eggs for eleven to fifteen days. Although only the female broods the nestlings, both parents feed and otherwise tend the young, which leave the nest after ten to eleven days. This species is parasitized by the brown-headed cowbird; the incidence of such parasitism is generally low but may be high in some areas.
Both the common name of this species and the genus to which it belongs honor Alexander Wilson, the Scottish-born "father of American ornithology" and a contemporary of John James Audubon.